Skeletal muscle blood flow is regulated by various mechanisms. 1 , 2 In general, nitric oxide, carbon dioxide, lactate, adenosine, adenosine triphosphate, and serotonin have vasodilatory effects, while endothelin and serotonin have vasoconstrictive effects. Although carbon dioxide has direct vasodilatory effects, an elevation in PaCO 2 also enhances sympathetic nervous system (SNS) activity, which leads to vasoconstriction with a net result of reduced blood flow at the skeletal muscle tissue level. 1 In anesthetized rabbits, increases in